SysPrep.exe is a tool located under c:\windows\system32\SysPrep folder. It can be used to “generalize” a Windows installation to be used for automated deployment instead of doing every fresh install from the ISO media.

I’ve done a fresh install of Windows Technical Preview build 9879, and attempted to install RSAT normally. That just worked:

In another fresh install of WinTP 9879 I tried using DISM:

That completed successfully as well.

Some have reported errors attempting to install RSAT for Windows TP. I’ve downloaded the latest Windows TP ISO and did a fresh install as a Gen 2 virtual machine on Hyper-V 2012 R2. I downloaded and installed RSAT without any issue. I wan not able to replicate the problem. However, here’s another way to try to install it: